linux-kernel - Re: [PATCH] cfg80211: Change an 'else if' into an 'else' in cfg80211_calculate_bitrate

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Date:   Fri, 22 Mar 2019 15:16:06 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Johannes Berg <johannes@...solutions.net>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] cfg80211: Change an 'else if' into an 'else' in cfg80211_calculate_bitrate_he

On Fri, Mar 8, 2019 at 12:57 AM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> When building with -Wsometimes-uninitialized, Clang warns:
>
> net/wireless/util.c:1223:11: warning: variable 'result' is used
> uninitialized whenever 'if' condition is false
> [-Wsometimes-uninitialized]
>
> Clang can't evaluate at this point that WARN(1, ...) always returns true
> because __ret_warn_on is defined as !!(condition), which isn't
> immediately evaluated as 1. Change this branch to else so that it's
> clear to Clang that we intend to bail out here.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/382
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  net/wireless/util.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/net/wireless/util.c b/net/wireless/util.c
> index e4b8db5e81ec..75899b62bdc9 100644
> --- a/net/wireless/util.c
> +++ b/net/wireless/util.c
> @@ -1220,9 +1220,11 @@ static u32 cfg80211_calculate_bitrate_he(struct rate_info *rate)
>         else if (rate->bw == RATE_INFO_BW_HE_RU &&
>                  rate->he_ru_alloc == NL80211_RATE_INFO_HE_RU_ALLOC_26)
>                 result = rates_26[rate->he_gi];
> -       else if (WARN(1, "invalid HE MCS: bw:%d, ru:%d\n",
> -                     rate->bw, rate->he_ru_alloc))
> +       else {
> +               WARN(1, "invalid HE MCS: bw:%d, ru:%d\n",
> +                    rate->bw, rate->he_ru_alloc);
>                 return 0;
> +       }

Reviewed-by: Arnd Bergmann <arnd@...db.de>

I independently came up with the same fix before I saw yours,
the only difference was that I avoided the extra curly braces
using

+       else
+               return !WARN(1, "invalid HE MCS: bw:%d, ru:%d\n",
+                            rate->bw, rate->he_ru_alloc);

to avoid the mix of bare if() and if() {}

      Arnd